Mixed turf

ABSTRACT

Provided is a mixed turf, positioned on a terrain. The mixed turf includes a synthetic turf lawn with natural turf placed within the synthetic turf lawn. The synthetic turf lawn also includes synthetic filaments configured to simulate blades of turf and a media including a non-biodegradable membrane sustaining the synthetic filaments. The media is positioned inside said terrain and is substantially draining, breathable and permeable to the roots of said natural turf. The media includes a textile made of a plurality of twines superposed and reciprocally woven together, each one having a base, which is periodically repeated along substantially the entire textile. Each twine has a base of different dimensions compared to the other twines along the extension plane of the textile.

The present invention relates to a mixed turf, partly synthetic and partly natural, suitable, for example, to cover sports fields or recreational, play or ornamental areas as described in the preamble of the first claim.

Similar lawns are described in the patent application WO-A-99/56523 and in U.S. Pat. No. 5,795,835.

For reasons of a practical and economic nature, the traditional coverings of sports fields and the like with natural turf lawns are often replaced by coverings in synthetic materials simulating natural turf lawns.

In particular, synthetic lawns simulating natural turf lawns are known of, comprising: a media, consisting of a polymeric membrane or backing, to which a plurality of filaments—they too polymers—extending vertically to simulate natural turf, are attached using a polymer resin in latex or polyurethane which makes the backing waterproof. To allow the runoff of the water to the underlying layers numerous holes are made in the backing. Such lawns further comprise a filling, superposed on the media, composed of granular material such as sand and so forth, which has a stabilising, protective and cushioning function. The filling and the media are permeable, or permit drainage and the runoff of excess water to the ground below. Mixed turfs are also known of, i.e. comprising structures in synthetic material mixed with natural turf which are more or less effective but with high production and/or maintenance costs of the turf lawn.

For example in the patent application WO-A-2006/008579 and in the U.S. Pat. No. 7,943,212 a technique is described of natural turf seeding on the filling above the media of a synthetic lawn. In such embodiments the media of the synthetic lawn is not biodegradable and acts as a barrier to the roots. It does not therefore allow the penetration of the natural turf roots in depth. The roots can in fact only grow horizontally inside the filling, which has a thickness of about 4-5 cm. Such lawns require frequent watering during the warmer months. Moreover, in hot and humid conditions the natural turf risks being stifled, favouring the development of fungal diseases. Generally, the persistence of excessive humidity combined with a rich biological activity in the soil, accelerates the consumption of oxygen present in the plant substrate. It thus promotes an anaerobic biological activity able to catch what little oxygen is present in the sulphur oxides, thereby releasing hydrogen sulphide (H₂S) which is a poisonous gas for the roots.

The monitoring of such lawns thus requires special attention and is very expensive. On account of the lack of deep roots the turf lawn risks drying out during the summer heat, and in the case of long wet periods risks being poisoning by the gas produced by anaerobic bacterial activity.

The U.S. Pat. No. 6,145,248 describes seeding techniques of natural turf on synthetic lawns which permit, from a theoretical point of view, the penetration of the natural turf root apparatus in depth thanks to the biodegradation of the synthetic lawn media. To allow this development, the media of the synthetic lawn is partly biodegradable to increase its porosity over time and allow the penetration of roots over time.

However, in this case, the attachment of the synthetic fibres to the support is not sufficient to withstand the tearing caused by players and thus the reinforcement of the lawn is limited and the player, in cases of exerting a greater force, pulls out the artificial fibres together with the natural turf sod. In addition, the product is not durable because, over time, part of the primary media degrades reducing its resistance and reducing even further the attachment of the synthetic fibres to the backing, thus the product disintegrates and the artificial fibres come away more easily, nullifying the benefits of mixed lawns. Lastly, the degradation of the materials used depends on many factors and in some cases, takes over two years, thus countering the need for rapid growth of the turf lawn, which is usually over 2-3 months: during the summer break of sports seasons. During the initial period, the penetration of the root apparatus in the underlying media is limited or absent due to poor air circulation in the soil due to the density of water depositing above the artificial lawn media thus forming an invisible water barrier which, in the case in which conditions of excess moisture persist, encourages anaerobic bacterial activity, releasing gases poisoning the roots as explained in the previous case. In any case, before the biodegradation of the backing, the geotropic angle of the root apparatus of the turf is in any case altered promoting a horizontal development which favours the formation of so-called “felt”, limiting even further the gas exchange between soil and air. The use of the field 2-3 months after seeding compacts the top layer even further and further facilitates the formation of “felt” on the surface which soon nullifies the benefits of the artificial turf. In fact, the remedy is difficult and requires working with machines which tend to also spoil the structure of the artificial turf. The system is not widely used on account of its high implementation and maintenance costs.

The U.S. Pat. No. 6,372,310 also describes the seeding techniques of natural turf on synthetic lawns which, from a theoretical point of view, allow the penetration of the root apparatus of the natural turf in depth through apertures in the media holding the synthetic filaments made by a broader weaving between the rows of weft and warp or by the degradation of some of the rows of the weft and warp over time. The present case differs from the previous, replacing the plurality of holes with large empty spaces made between the groups of rows of warp and weft woven in a spaced manner or, as happens in some cases, which tend to form with the partial use of biodegradable material over time. The weaving of the filaments in the intersection points of the media leaves more space for the growth of natural turf on the surface and is less expensive because it uses less plastic. However, the penetration of the root apparatus in the underlying media is limited for the same reasons mentioned above for the previous system. The hold of the turf filaments in the media is not guaranteed according to laboratories specialised in artificial turf. In fact by closely observing the structure the poor hold of the fibres in the support may be noted, the attachment of the fibres is performed by spreading a latex resin on the bottom at the groups of rows containing the artificial turf fibres only, waterproofing most of the backing. The groups of rows with artificial fibres are alternated with the groups of rows made partly with biodegradable fibres and it is doubtful whether a stable textile can be made by eliminating a group of weft and/or warp fibres. Soon the natural turf dies before the textile allows the development of the roots in depth on account of the poisoning by the gases produced by the anaerobic bacterial activity.

Another type of technology, related mainly to soccer fields, provides for the insertion on site of artificial yarns in the natural turf field: approximately 20 million artificial yarns for a sports field of 7000 m² up to 20 cm deep in sandy soil to better withstand the “traffic” from playing football. Although this method respects the agronomic principles for the growth of natural turf, it is restricted to sandy soils, and is complex and expensive because it requires special machinery with a low output with high maintenance costs. In stadiums the organisation of major events, such as concerts, coincides with the summer period and the covering of the lawn with heavy plates, suitable for supporting the stage make the natural turf die completely. The reseeding of turf lawns in stadiums takes a long time which is often not compatible with playing requirements, it is thus preferred to remove the clods of turf and lay a new turf lawn. The presence of artificial yarns in the first 20 cm of the soil also requires the removal of the entire sandy substrate, which must be disposed of as special waste. The possible separation of the artificial turf from the sand is also expensive. It is understood that merely the movement of the material has a significant impact on the times and costs of laying a new lawn and the new installation of new artificial fibres.

Lastly, all the drainage systems of synthetic lawns, mixed lawns and even the numerous turf lawns have the drawback of using drainage systems which reroute the rainwater to the sewer system or directly into groundwater through soakaways with all the consequent risks. It is no coincidence that natural turf lawns for playing fields and the like, contrary to the country grassland, are considered impermeable soils.

In this situation the technical purpose of the present invention is to devise being able to substantially overcome the drawbacks mentioned above. Within the sphere of said technical purpose one important aim of the invention is to make a mixed turf which is resistant and with high quality features.

Another important purpose of the invention is to obtain a mixed turf which is economical and easy to install and maintain.

Yet another purpose of the present invention is to make a mixed turf which permits a rapid infiltration of the water in the drainage layers without weighing on capacity of the drainage system.

The technical purpose and specified aims are achieved by as claimed in the appended claim 1.

Preferred embodiments are evident from the dependent claims.

The characteristics and advantages of the invention are clearly evident from the following detailed description of a preferred embodiment thereof, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic cross-section of the mixed turf according to the invention;

FIG. 2 is an exploded schematic cross-section of a portion of a first example of a mixed turf according to the invention;

FIG. 3 is a schematic diagram of a portion of the mixed turf according to the invention.

With reference to said drawings, reference numeral 1 globally denotes the mixed turf according to the invention.

It is appropriately part of a terrain 10 further comprising a substrate 11, described below.

The lawn 1 is suitable to form a substantially turf surface, for example a surface of a playing field, and preferably of a soccer pitch, or even appropriately a rugby, American football pitch or hockey field or otherwise, or even an area for recreational, decorative, ornamental purposes and so forth.

The mixed turf 1 comprises a synthetic turf lawn 2 and natural turf 3 placed within said synthetic turf lawn, as described below.

In detail the synthetic turf lawn 2 comprises a media 4, described below, and a plurality of synthetic filaments 5, simulating natural turf.

Appropriately the media 4 is draining and above all breathable both in the dry and wet state. The media 4 is also advantageously non-biodegradable, and more preferably completely non-biodegradable, to maintain the hold of the filaments 5 unchanged over time. Furthermore, said layer does not provide, as happens traditionally, for a coating on the bottom with polymers such as polyurethane or latex which make the media waterproof.

The media 4 has, in addition, appropriately, an irregular and indented surface morphology which increases the upper area of said media 4 increasing the interaction surface with any liquids and, consequently, increasing the permeability of said media 4.

In particular jagged surfaces minimise the formation of surface tension phenomena possible on smooth media, and also the formation of a water barrier by the force of the density of water.

The media 4 thus preferably has a three-dimensional conformation in which the apertures are not regularly arranged along a continuous surface, but are arranged on surfaces with different inclinations.

The media 4 as a whole is substantially permeable to water in its totality and above all breathable, allowing the circulation of gases in the soil. The term “in its totality” means that the whole surface, on a macroscopic scale, of the media has the characteristics of permeability and breathability, given by the choice of the microscopic characteristics of the media. In particular, the three-dimensional shape of the media which prevents the formation of a water barrier caused by the density of the water above the media.

Furthermore, the media 4, thanks to the characteristics described, allows the passage of the roots substantially across the entire surface and thus again in its totality.

In particular, the media 4 comprises a textile 40.

The textile 40 is preferably made of non-biodegradable polymeric material and more preferably of polyester or alternatively polypropylene or polyethylene, preferably high density.

It is also preferably made of a plurality of twines superposed and reciprocally woven together, each one having a base which repeats periodically substantially along the entire textile. In addition, each twine has a base of different dimensions compared to the other twines along the extension plane of said textile 40. In particular, it consists of three, and alternatively more than three or even only two twines each with a base, i.e. a portion of minimum size that is repeated periodically substantially along the entire textile 40, of different dimensions, in particular width, in the plane of the textile. This solution makes the twines with bases of a larger dimension periodically overlap the twines with a smaller base creating a three-dimensional, jagged surface as described above.

The textile 40 preferably also has apertures having mean dimensions of the main orthogonal diameters, of 2 mm to 0.5, more preferably 1.5 mm to 0.5 mm. In particular, the apertures have different mean dimensions of the main orthogonal diameters and the lesser diameter has a length of 0.6 mm to 0.4 mm so as to prevent the passage of the sand and at the same time permit the passage of the roots.

The weight of the textile 40 is preferably between 20 g/m² and 350 g/m² and more preferably between 250 g/m² and 350 g/m².

Said textile 40 may also be starched with vinyl or acrylic glue.

Preferably the textile 40 is a warp-knitted textile made on a warp-knitting loom, i.e. a Raschel type machine. The terms and the illustrations used below are thus interpretable by a person skilled in such art, i.e. of warp-knitted textiles. Said warp-knitted textiles are woven in a single direction, the warp, preferably having a vertical direction in weaving and vertical direction in FIG. 3.

Preferably the warp-knitted textile is made along three bars of needles and each bar produces a twine with a base different in width so that said plurality of twines overlap. In particular, the different width is obtained by means of different dimensions of the base.

In detail, as shown in FIG. 3 there are three twines, each made by a bar of needles, of which a first twine 41 (indicated by the continuous line in FIG. 3) with a frequency of one needle that repeats every two columns of needles and preferably with all open stitches, a second twine 42 (indicated by the dotted line in FIG. 3), preferably with needles in a staggered position and preferably all with closed stitches, which has a frequency of two needles, and a third twine 43 (indicated by the dashed-dotted line in FIG. 3) with a frequency of five needles and preferably all with open stitches. Such textile 40 is preferably made on machines with a needle frequency of between 16 and 18 needles per inch. The yarns composing the textile, preferably in polyester, may have a mass of between 600 dtex and 800 dtex. The synthetic filaments 5 are appropriately connected to the textile 40 through tufting, a technique known per se, they are also preferably polyethylene.

They may also be attached to the textile 40 through connection at the bottom of the textile 40 of a nonwoven polyester 44 preferably partially melted onto the textile 40 and pressed against said textile 40 using a hot roller, in particular at a temperature between 180° C. and 200° C. Said non-woven textile 44 preferably has a weight of 20 g/m² and 300 g/m² and more preferably between 100 g/m² and 220 g/m², and/or preferably a density of between 1 g/cm³ and 3 g/cm³ preferably between 1.2 g/cm³ and 1.5 g/cm³.

Alternatively or in addition, the synthetic filaments 5 may also be attached to the textile using a coating of glue, suitable not to close the apertures of the textile 40 and of the media 4, in particular acrylic glue or the like in an amount between 80 and 150 g/m².

Preferably, the complete media 4 is suitable to obstruct or limit the passage of medium sand and other granular material with dimensions greater than 250 μm, which is preferably the filling material of the synthetic lawn 2.

More particularly, the synthetic filaments 5 are preferably sewn by means of said tufting and are preferably arranged in groups of filaments 5 a. They have appropriately a length between 4 cm and 7 cm and are preferably in latest generation softer polyethylene with special shapes or ribs for added resilience. The quantity of synthetic filaments 5 is optimised so that there is space for the growth of the natural turf 3. In particular the synthetic filaments 5 are arranged in parallel lines spaced at distances ranging from 10 mm to 60 mm and more preferably from 15 mm and 45 mm or otherwise. In addition, in some areas, for example in the busiest areas of a soccer pitch such as the goalkeeper's area, the synthetic filaments 5 can be arranged more thickly. In particular, the synthetic filaments 5 do not exceed in density of arrangement on the ground 10%-50% of the density of arrangement of the natural turf 3 having the desired density.

In a second example, the media 4 consists of two membranes in non-woven, with similar characteristics to that previously described but a heavier weight, in particular between 200 and 400 g/m² and more preferably between 250 and 350 g/m², and also starched to give it greater strength and stability, into which the artificial yarns 5 are fixed with tufting.

The attachment is performed by means of hot welding with a second thin, non-woven, with characteristics similar to those described above for the first example or by applying a glue, covering only the row of points for a maximum of 25% of the surface, as in the previous example.

This last media 4 has a large capacity to absorb water providing a buffering effect, very useful for saving even more and sustaining the plant especially in hot climates.

The media 4 as a whole is substantially permeable to water in its totality, breathable, and permeable to the roots, i.e. suitable to permit the passage of the roots and allow the free circulation of the gases in the soil. The term “in its totality” means that the entire surface of the media, on a macroscopic scale, has the characteristics of permeability and breathability, given by the choice of the microscopic characteristics of the media. In particular, the three-dimensional shape of the media 4 described which prevents the formation of a water barrier caused by the density of the water above the media.

The turf terrain 10 further comprises an upper layer 7, placed above the media 4, and a lower layer 8, which supports the media 4 and is therefore in contact with said support 4 and with the top layer 7.

The top layer 7 is preferably composed of a mixture of sandy material and organic material, in particular deriving from plants, preferably in granular and/or fibrous form.

The sand has a diameter between 0.05 mm and 2 mm, preferably between 0.25 and 1 mm and is present in percentages preferably between 50% and 90% of the total volume of the upper layer 7.

The organic material preferably comprises granules of cork, preferably of the “gentle”type, i.e. used for corks for bottles and the like. It is preferably present in the granules with diameter between 0.5 mm and 1.5 mm and appropriately in percentages ranging between 5% and 30%.

The organic material preferably also, or only, comprises coconut fibres appropriately in percentages ranging between 5% and 30% and preferably smaller than 10 mm.

The upper layer 7 preferably has a thickness between 0.5 cm and 8 cm and more preferably between 2 cm and 4 cm and leaves a free portion of synthetic filaments 2 of length preferably between 1.5 cm and 3 cm. Furthermore, the layer 7 enables drainage and serves to improve the texture of playing field, in particular to support the player while playing, at the same time favouring the growth of the natural turf lawn.

The lower layer 8 is a plant draining layer in contact with the substrate 11, it is preferably of the same type and composed of the same material as the upper layer 7. If necessary the lower layer 8 may contain greater sizes of the granular and fibrous elements.

Additional substrates of crushed stone or other draining materials may be arranged between the lower layer 8 and the substrate 11.

The turf lawn 1 further comprises natural turf 3 as previously specified. The natural turf 3, in optimal conditions, is arranged on the lawn 1 together with the synthetic lawn 2 and is preferably present on average from about 2 to 10 times more than the average amount on the terrain 10 of the synthetic lawn 2. The amount can be measured visually, for example by comparing groups of synthetic filaments 5 and natural turf 3 tussocks. The natural turf is supported by the top surface of the upper layer 7 and comprises a root apparatus which extends advantageously throughout the top layer 7, passes through the media 4 and extends along the lower layer 8 (FIG. 1) and preferably also along part of the substrate 11.

The substrate 11 consists of the existing terrain, such as farmland or similar. It comprises a drainage system consisting of trenches and channels of various sizes and shapes, as illustrated in FIG. 3.

The mixed turf 1 according to the invention, and the method described achieve important advantages. In fact, the applicant has surprisingly discovered that the prior structures comprising media consisting of substantially impermeable membranes and provided with apertures or holes of macroscopic size did not allow transpiration and gas exchange between the soil and the air on account of the water density and surface tension phenomena which made the water deposit above the media of the artificial lawn and obstruct said holes or apertures. The applicant then unexpectedly discovered that the media 4 described, with permeability and breathability given by the microscopic characteristics of the media 4 along the entire surface of said media 4, permitted the passage of water and air, contrary to what might have seemed at first sight. This advantage is due in particular to the jagged and three-dimensional surface described and in particular to the textile 40 described.

The lawn 1 thus permits the proliferation of the root apparatus in depth and the attachment to the media of the natural turf 3 by means of its root apparatus. Consequently, the combination of the synthetic lawn 2 and natural turf 3 described makes the natural turf 3 resistant to summer drought, trampling and horizontal playing tensile stress and provides high comfort of play.

In addition, the size of the apertures of the textile 40 described prevents sand from entering into the textile 40 and limiting the permeability of the media 4. The media 4 thus has a very high durability and does not degrade as a result of the obstruction caused by sand and the like.

Specifically, the artificial yarns protect the leaf apparatus and, above all, the corona, the most delicate part of the plant. At the same time, the root apparatus grows vigorously right from the first period of growth, grows in depth and anchors itself in the media 4 forming a consistent clod of mixed turf resistant to trampling and the sliding of players. Damage to the field by use is limited so as to maintain an even and safe surface for the game, at the same time saving on extraordinary maintenance costs.

The mixed turf 1 is also simple and relatively inexpensive to install.

It is therefore easier to increase the intervals between one irrigation and the next, which favours a rich and deep rooting, fundamental to increasing the resistance of the natural lawn.

Variations may be made to the invention without departing from the scope of the inventive concept expressed in the independent claims and by the relative technical equivalents. 

1. A mixed turf, positioned on a terrain and comprising: a synthetic turf lawn; and natural turf placed within said synthetic turf lawn, said synthetic turf lawn comprising synthetic filaments to simulate blades of turf and a media comprising a non-biodegradable membrane sustaining said synthetic filaments, said media being positioned inside said terrain and being in its entirety substantially draining, breathable and permeable to the roots of said natural turf, said media including a textile that comprises a plurality of twines superposed and reciprocally woven together, each one having a base, which is a portion of minimal dimension which is periodically repeated along substantially the entire fabric, which repeats periodically substantially along the entire textile, and each of said twines has a base of different dimensions compared to the other said twines along the extension plane of said textile.
 2. The mixed turf according to claim 1, wherein said textile comprises three superposed twines.
 3. The mixed turf according to claim 1, wherein said textile comprises apertures having mean dimensions of the main orthogonal diameters, of from 2 mm to 0.5 mm.
 4. The mixed turf according to claim 1, wherein said textile comprises apertures having different mean dimensions of the main orthogonal diameters and the lesser diameter has a length of from 0.6 mm to 0.4 mm so as to prevent the passage of the sand and permit the passage of the roots.
 5. The mixed turf according to claim 1, wherein said textile comprises polyester threads.
 6. The mixed turf according to claim 1, wherein said textile is starched.
 7. The mixed turf according to claim 1, wherein said textile is a warp-knitted type textile.
 8. The mixed turf according to claim 1, wherein said media comprises a non-woven textile connected to the lower part of said textile and configured to connect said synthetic filaments to said media.
 9. The mixed turf according to claim 8, wherein said non-woven textile has a density of from 1 g/cm³ to 3 g/cm³.
 10. The mixed turf according to claim 1, wherein said media comprises a coat of glue configured not to close the apertures of said textile and, on the lower part of said textile configured to connect said synthetic filaments to said media. 